Structure and dynamics of atactic Na+-poly(acrylic) acid (PAA) polyelectrolyte in aqueous solution in dilute, semi-dilute and concentrated regimes
TL;DR: In this paper, structural and dynamic properties of aqueous solution of atactic poly(acrylic) acid in dilute, semi-dilute and concentrated regimes were studied by fully atomistic molecular dynamics simulati...
Abstract: Structural and dynamic properties of aqueous solution of atactic poly(acrylic) acid (PAA) in dilute, semi-dilute and concentrated regimes were studied by fully atomistic molecular dynamics simulati...
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TL;DR: In this paper, the authors investigate theoretically charge regulation of weakly dissociating polyacids by potentiometric titration of their aqueous solutions, by treating deprotonation and cation binding to the polyacid as reversible reactions in their model, the ionization constant of acid groups along the polyacid chain is adjusted from its intrinsic value by electrostatic correlations.
20 citations
TL;DR: It is observed that at low polymer concentrations PDMAEMA chains adopt a stiffer and slightly extended conformation due to excluded-volume effects and electrostatic repulsions within the polymer chains, as the polymer concentration increases above 20 wt %, and adopt more flexible conformations.
Abstract: A combined experimental and molecular dynamics (MD) study is performed to investigate the effect of polymer concentration on the zero shear rate viscosity η0 of a salt-free aqueous solution of poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA), a flexible thermoresponsive weak polyelectrolyte with a bulky 3-methyl-1,1-diphenylpentyl unit as the terminal group. The study is carried out at room temperature (T = 298 K) with relatively short PDMAEMA chains (each containing N = 20 monomers or repeat units) at a fixed degree of ionization (α+ = 100%). For the MD simulations, a thorough validation of several molecular mechanics force fields is first undertaken for assessing their capability to accurately reproduce the experimental observations and established theoretical laws. The generalized Amber force field in combination with the restrained electrostatic potential charge fitting method is eventually adopted. Three characteristic concentration regimes are considered: the dilute (from 5 to 10 wt %), the semidilute (from 10 to 20 wt %), and the concentrated (from 20 to 29 wt %); the latter two are characterized by polymer concentrations cp higher than the characteristic overlap concentration cp*. The structural behavior of the PDMAEMA chains in the solution is assessed by calculating the square root of their mean-square radius of gyration «Rg 2»0.5, the square root of the average square chain end-to-end distance «Ree 2»0.5, the ratio «Ree 2»/«Rg 2», and the persistence length Lp. It is observed that at low polymer concentrations, PDMAEMA chains adopt a stiffer and slightly extended conformation because of excluded-volume effects (a good solvent is considered in this study) and electrostatic repulsions within the polymer chains. As the polymer concentration increases above 20 wt %, the PDMAEMA chains adopt more flexible conformations, as the excluded-volume effects seize and the charge repulsion within the polymer chains subsides. The effect of total polymer concentration on PDMAEMA chain dynamics in the solution is assessed by calculating the orientational relaxation time τc of the chain, the center-of-mass diffusion coefficient D, and the zero shear rate viscosity η0; the latter is also measured experimentally here and found to be in excellent agreement with the MD predictions.
13 citations
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TL;DR: In this paper, the authors reported self-diffusion and viscosity data for sodium polystyrene sulfonate (NaPSS) in semidilute salt-free aqueous solutions measured by pulsed field gradient NMR and rotational rheometry respectively.
Abstract: We report chain self-diffusion and viscosity data for sodium polystyrene sulfonate (NaPSS) in semidilute salt-free aqueous solutions measured by pulsed field gradient NMR and rotational rheometry respectively. The observed concentration dependence of $\eta$ and $D$ are consistent with the Rouse-Zimm scaling model with a concentration dependent monomeric friction coefficient. The concentration dependence of the monomeric friction coefficient exceeds that expected from free-volume models of diffusion, and its origin remains unclear. Correlation blobs and dilute chains with equivalent end-to-end distances exhibit nearly equal friction coefficients, in agreement with scaling. The viscosity and diffusion data are combined using the Rouse model to calculate the chain dimensions of NaPSS in salt-free solution, these agree quantitatively with SANS measurements.
11 citations
TL;DR: Molecular dynamics simulations are used to study structure and dynamics of poly(vinyl alcohol) and water in aqueous solution as a function ofconcentration at different temperatures in the range 278.
Abstract: Molecular dynamics simulations are used to study structure and dynamics of poly(vinyl alcohol) and water in aqueous solution as a function ofconcentration at different temperatures in the range 278...
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155 citations
"Structure and dynamics of atactic N..." refers methods or result in this paper
...The result obtained from our simulations, of a decrease in Na ion diffusion with increase in f is in good agreement with that experimental study [82]....
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...charge density f ) A decrease in Na ion diffusion coefficient with increase in degree-of-neutralisation of PAA chains, in aqueous solution of atactic PAA in sodium hydroxide was observed using radioactive Na ion tracer [82]....
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TL;DR: In this article, the authors present results of the molecular dynamics simulations of salt solutions of polyelectrolyte chains with number of monomers N = 300, and show that the chain size decreases with increasing the salt concentration as R ∝ I−1/5.
Abstract: We present results of the molecular dynamics simulations of salt solutions of polyelectrolyte chains with number of monomers N = 300. Polyelectrolyte solutions are modeled as an ensemble of bead–spring chains of charged Lennard-Jones particles with explicit counterions and salt ions. Our simulations show that in dilute and semidilute polyelectrolyte solutions the electrostatic induced chain persistence length scales with the solution ionic strength as I–1/2. This dependence of the chain persistence length is due to counterion condensation on the polymer backbone. In dilute polyelectrolyte solutions the chain size decreases with increasing the salt concentration as R ∝ I–1/5. This is in agreement with the scaling of the chain persistence length on the solution ionic strength, lp ∝ I–1/2. In semidilute solution regime at low salt concentrations the chain size decreases with increasing polymer concentration, R ∝ cp–1/4, while at high salt concentrations we observed a weaker dependence of the chain size on th...
153 citations
"Structure and dynamics of atactic N..." refers background in this paper
...The addition of alkali or alkaline earth salts to polyelectrolyte solutions results in screening of electrostatic interactions between the chains [5]....
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TL;DR: In this article, Monte Carlo simulations, experimental titrations and fluorescence correlation spectroscopy experiments were used to investigate the conformational and electrical properties of polyacrylic acids (PAA).
150 citations
"Structure and dynamics of atactic N..." refers background or result in this paper
...The physicochemical actions in an aquatic ecosystem are affected by natural anionic polyelectrolytes of which PAA serves as a synthetic analogue [19,20]....
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...A combined study involving potentiometric titration and bead-spring Monte-Carlo simulations was carried out as a function of molecular weight in order to investigate the dependence of conformation chainsize on solution pH [19]....
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...Studies have shown a strong dependence of PAA conformational size on pH [19,21]....
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...This behaviour is in agreement with well-known results of potentiometric titrations and Monte-Carlo simulations of PAA aqueous solution carried out as a function of pH [19]....
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...PAA is a weak polyelectrolyte and is fairly soluble in polar solvents such as water [19]....
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123 citations
"Structure and dynamics of atactic N..." refers background in this paper
...In the past few decades, numerous research works have been reported on experimental [1,2,13,14], computational [1–8] and theoretical aspects [1,4,15] of polyelectrolyte solutions....
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